This grant proposal is a continuation of the program for the systematic study of psychotropic drugs on the Children's Service of Bellevue Psychiatric Hospital, New York. The scope of work has been expanded and specific projects outlined with an effort for methodological improvement. We wish to concentrate our efforts on preschool age autistic children and other severely disturbed hospitalized children of school age. We wish to evaluate the therapeutic effectiveness and safety of new drugs in these children, to coordinate behavioral biological changes on and off drugs, and to determine bioavailability of drugs. In addition, we shall evaluate critically the efficacy of behavior therapy with specific emphasis on language acquisition, with or without drug treatment in young autistic children. Individual patients will be followed longitudinally to evaluate the efficacy and safety of long-term drug maintenance as well as long-term outcome of drug treatment and somatosexual maturation. The studies will be carried out in order to develop a more rational approach in pharmacotherapy for this population, to delineate biologically more meaningful diagnostic categories or subgroups, and to define "drug responders."